(1) Field of the Invention
The present invention relates to an axial multi-piston swash-plate-type compressor used in, for example, an air-conditioning system incorporated in a vehicle such as an automobile.
(2) Description of the Related Art
As disclosed in, for example, Japanese Unexamined Publication No. 3-92587, an axial multi-piston swash-plate-type compressor comprises: front and rear cylinder blocks axially combined to form a swash-plate chamber therebetween, the combined cylinder blocks having the same number of cylinder bores radially formed therein and arranged with respect to the central axis thereof, the cylinder bores of the front cylinder block being aligned and registered with the cylinder bores of the rear cylinder block, respectively, with the swash plate chamber intervening therebetween; double-headed pistons slidably received in the pairs of aligned cylinder bores, respectively; front and rear housings fixed to front and rear end faces of the combined cylinder blocks through the intermediary of front and rear valve plate-assemblies, respectively, the front and rear housings each forming a suction chamber and a discharge chamber together with the corresponding one of the front and rear valve-plate assemblies; a rotatable drive shaft arranged so as to be axially extended through the front housing and the combined cylinder blocks; and a swash plate securely mounted on the drive shaft within the swash plate chamber and engaging with the double-headed pistons to cause these pistons to reciprocate in the pairs of aligned cylinder bores, respectively, by the rotation of the swash plate. The front and rear cylinder blocks, the front and rear valve-plates and the front and rear housings being axially and tightly assembled as an integrated unit by a plurality of long screw bolts extended therethrough.
The front and rear valve-plate assemblies in particular have substantially the same construction in that each comprises: a disc-like member having sets of ports, each set having one suction port and one discharging port, the ports being able to communicate with the corresponding one of the cylinder bores of the front or rear cylinder block; an inner valve sheet attached to the inner side surface of the disc-like member and having suction reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding suction port of the disc-like member; an outer valve sheet attached to the outer side surface of the disc-like member and having discharge reed valve elements formed integrally therein, each of which is arranged so as to open and close the corresponding discharge port of the disc-like member; and a gasket attached to the outer valve sheet and hermetically engaged with an end face of a partition wall of the front or rear housing defining the suction and discharge chambers. Each of the front and rear valve plate assemblies is also provided with suction openings aligned with passages formed in the front or rear cylinder block, respectively, whereby the suction chambers formed by the front and rear housings are in communication with the swash plate chamber to which a refrigerant is supplied from an evaporator of an air-conditioning system, through a suitable inlet port formed in the combined cylinder blocks.
In the swash-plate-type compressor as mentioned above, the drive shaft is driven by the engine of a vehicle, such as an automobile, so that the swash plate is rotated within the swash plate chamber, and the rotational movement of the swash plate causes the double-headed pistons to be reciprocated in the pairs of aligned cylinder bores. When each piston is reciprocated in the aligned cylinder bores, a suction stroke is executed in one of the aligned cylinder bores and a compression stroke is executed in the other cylinder bore. During the suction stroke, the suction reed valve element is opened and the discharge reed valve element is closed, whereby the refrigerant is introduced from the suction chamber to the cylinder bore through the suction port. During the compression stroke, the suction reed valve element concerned is closed and the discharge reed valve element concerned is opened, whereby the introduced refrigerant is compressed and discharged from the cylinder bore into the discharge chamber through the discharge reed valve element. The compressed refrigerant is fed from the discharge chamber to the condenser of the air-conditioning system. The refrigerant includes a lubricating oil mist, and the movable parts of the compressor are lubricated with the oil mist during the operation. Also, the oil mist appears on the suction and discharge reed valves, and serves as a liquid-phase seal when each of the reed valve is closed.
Just after the suction stroke is initiated, i.e., just after the head of the piston is from the top dead point toward the bottom dead point, the suction reed valve cannot be immediately opened because the suction reed valve is adhered to the valve seat with the liquid oil, and because a resilient force of the suction reed valve must be overcome before the refrigerant can be introduced from the suction chamber to the cylinder bore through the suction port. Namely, the suction reed valve cannot be opened until a differential between the pressures in the cylinder bore and the suction chamber exceeds a certain level. Further, the suction reed valve may be prematurely closed before the suction stroke is finished, because the reed valve has a tendency toward being returned from the open position to the closed position due to the resilient force thereof. Accordingly, a sufficient amount of the refrigerant cannot be delivered to the cylinder bore during the suction stroke, and thus the conventional compressor cannot exhibit fully the operational performance thereof.
Also, in the compressor as mentioned above, a plurality of through passages is formed in the front and rear cylinder blocks to feed the refrigerant from the swash plate chamber to the suction chamber and to communicate the front and rear discharge chambers with each other. Of course, the mechanical strength of the cylinder blocks is weakened by the formation of the through passages therein. Accordingly, the cylinder blocks must have a large size, resulting in a bulkiness of the compressor.